The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In general, a microelectromechanical system (MEMS) microphone is a device that converts an audio signal into an electrical signal and MEMS microphone is manufactured with a semiconductor batch process.
Compared with an electrets condenser microphone (ECM) applied to most vehicles, the MEMS microphone has excellent sensitivity and low performance variations of products. Also, it can be microminiaturized and endurable to a change in an environment such as heat, humidity, and the like. Thus, recently, the development of the MEMS microphone is gradually replacing the ECMs.
In order to increase sensitivity that is one of the most important performance indices of the MEMS microphone, research into a reduction in rigidity or maximization of a sensing area has been conducted.
FIG. 1 is a cross-sectional view schematically showing a structure of a conventional commercial MEMS microphone.
Referring to FIG. 1, a conventional MEMS microphone has a structure in which a diaphragm 2 and a fixed membrane 3 are formed on a substrate 1 at regular intervals and a sacrificial layer 4 is supported therebetween. A plurality of holes 3h of the fixed membrane 3 for air inflow are formed in the fixed membrane, and an air layer 5 is formed between the diaphragm 2 and the fixed membrane. Vibration displacement of the diaphragm 2 vibrated by a sound pressure input through the substrate hole 1h is sensed by the fixed membrane 3.
The fixed membrane holes 3h serves as a path for removing the sacrificial layer 4 between the fixed membrane 3 and the diaphragm 2. The fixed membrane holes 3h serves to reduce air damping when the diaphragm 2 is vibrated by the sound pressure.
The air damping means that vibration of the diaphragm 2 is absorbed by the air and its pressure and the vibration displacement is suppressed. It is referred to as an air damping effect that sensitivity deterioration occurs due to suppression of the vibration displacement.
However, in the conventional art, a sensing area is reduced when the number of the fixed membrane holes 3h is increased in order to reduce the air damping of the fixed membrane 3. As a result, the sensitivity is decreased.
Therefore, a new concept structure that can improve the sensitivity may be desired.
The related information is further disclosed in Korean Patent Publication No. 10-2014-0028467.